Please add a doc-block briefly describing what this does.  Also, this doesn't seem to be used right now, but I'm assuming that code doesn't exist yet (or forgot to get "git add"ed?)  I think a useful explanation would be:

Convenience wrapper around MailParser to allow us to hackily reuse its body part decoding logic (ex: base64, quoted-printable) functionality.  (Normally MailParser only wants to parse entire messages.)

When passing our 'parse' method as an event listener, be sure to call bind() on it.